Rapid bacteria detection in drinking water samples with on-chip Mach-Zehnder Interferometers

Drinking water contamination by pathogenic bacteria poses a great danger for public health, since according to WHO 5 million deaths are associated to water related diseases annually. To safeguard drinking water quality, several techniques for bacteria detection, such as culturing and plating, ELISA and DNA-based methods have been developed; which, however, are laborious and time consuming. In this work, we present a miniaturized immunosensor for the rapid, simultaneous label-free determination of bacteria in drinking water. The sensor consists of ten broad-band Mach-Zehnder interferometers (MZIs) integrated on silicon chip along with their corresponding light sources. For the analysis, the MZIs sensing areas were biofunctionalized with bacteria membrane antigens. Then, bacteria mixtures with anti-bacteria specific antibodies were pumped over the chip followed by biotinylated anti-species specific antibody and streptavidin solutions. Binding of antibodies onto the MZI-immobilized antigen, changes the effective refractive index over the MZI area causing an interference spectrum shift which is monitored continuously by an external spectrometer. Due to the short analysis time (12 min), the low detection limits achieved (